This invention concerns foot rolls for continuous casting. To be more exact, the foot rolls of this invention are positioned immediately downstream of the ingot mould employed in continuous casting plants.
Such ingot moulds are located downstream of a tundish and upstream of a discharge roller conveyor.
Continuous casting ingot moulds contain a crystallizer, or downstream mould portion, of a pre-set section which upon start-up cooperates with a movable bottom, to which is fitted a pinetree-shaped element for attachment to the cast liquid metal.
This movable bottom is connected to a starter bar that cooperates with a discharge roller conveyor positioned downstream of the mould so as to draw the ingot being formed.
It is known that the ingots being formed and leaving the mould are additionally cooled by suitable cooling means that act directly on the ingot being formed.
The skin of the ingot at the outlet of the crystallizer may be thin, and therefore the ingot has to be suitably contained by the foot rolls and conveyed to the discharge roller conveyor.
These foot rolls form series of two, three, four or more succesive layers of assemblies of rolls cooperating together. Each assembly consists of idler rolls able to rotate about their respective supporting shafts.
These idler rolls are positioned in such a way as to come into contact with the whole perimeter of the ingot being formed so as to prevent non-homogeneous pressures.
The supporting shafts which bear the idler rolls are upheld by suitable uprights.
The state of the art generally employs two solutions:
bearings that bear the idler rolls, whereby the idler rolls rotate about their respective supporting shafts secured to the uprights; PA1 bearings that bear the supporting shaft, whereby the idler rolls are integrally secured to their respective supporting shafts able to rotate in relation to the uprights.
The solution whereby the bearings bear the idler rolls is generally employed because it is safer and less expensive.
From a dynamic point of view the foot rolls are little stressed but are heavily stressed from a thermal point of view; for this reason the cooling means spray the ingot being formed with water under high pressure and at the same time also bathe and cool the idler rolls and the respective supporting shafts.
So as to reduce the thermal shock further, suitable inner conduits coaxial with the supporting shafts are included, and through these conduits a cooling liquid consisting of water is passed.
In the state of the art each supporting shaft includes at the ends of each inner conduit an inlet and an outlet, the conduits being connected in series with flexible tubes.
These flexible tubes are located in a zone in which a breakage of the skin of the ingot being formed brings the liquid metal into contact with the flexible tubes, thus causing wear of the tubes and impairing their functioning.
Moreover, the cooling systems for the foot rolls of the state of the art do not ensure efficient cooling of the idler rolls, which thus become worn excessively.